Calligra Sheets column/row limits
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Restrictions by sizeof(int); i <= 2^31-1:
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- PointStorage.h:
    QVector<T>'s index is an int; Provides access to all cells.
    Therefore, sizeof(col)*sizeof(row) <= sizeof(int); sizeof(col/row) = 2^16;
    As QVector and QRect depend on (signed) int: max(col/row) = 2^15-1
        -> Global.h: KS_colMax = 2^15-1, KS_rowMax = 2^15-1
        -> Cell::Private: restriction by bit fields; 16 bits per column/row
        -> Region.h:
            uint qHash(QPoint); column coded in first 16 bits, row in the last
            Can be extended by just considering the last 16 bits of the col/row,
            even if bigger than 16 bits. Leads to hash collisions, but works.
        -> Cell.h:
            uint qHash(Cell); column coded in first 16 bits, row in the last
            Can be extended by just considering the last 16 bits of the col/row,
            even if bigger than 16 bits. Leads to hash collisions, but works.
        -> Column-/RowCluster: restricted to 2^15
            Can be extended easily by increasing one of the cluster levels,
            preferably the first.
    The limitation could be lifted, if a clustered array is used in PointStorage
    and PointStorage::data(int), ::col(int), ::row(int) get ported to qint64.
- QRect: based on int

Minor issues, that would need adjustment:
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- Headers.h: The RowHeader's width should display all row numbers correctly.
- Sheet: QHash<QString, QRegion> *StyleRegion; QRegion is restricted (on Windows 95/98/ME)

Other restrictions:
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- Rect-/StyleStorage.h:
    Based on QRectF, which is based on qreal (double or float). Numbers range
    from 0..2^52 or 0..2^23, resp., with an exponent of 0, i.e. mantissa * 2^0.
    Other exponents lead to "integer gaps"; step size != 1 (Actually, if a
    number could be expressed with an other exponent without inaccurrancy, this
    will be done, but that does not matter here. It's possible to encode it with
    e=0.)

Performance:
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- Copying cell contents is done cell-by-cell. PointStorage is arranged in rows,
  i.e. copying of rows could be optimized, but for columns a traversal of all
  occupied columns is necessary.
  Go the same way as in Cluster and follow a two-levelled approach? Could be an
  option for further optimizations for copying areas, but would give headaches
  at the cluster boundaries.
